Recently, an adaptive front lighting system (AFS) for a vehicle is used which controls a direction of light from a head light of the vehicle so that the head light illuminates a position which a driver of the vehicle wants to look at. The AFS has a swivel control function, in which an azimuth angle (hereafter referred to as a swivel angle) of the direction of the light is changed around a vertical axis of the vehicle.
More specifically, in the swivel control function, the AFS calculates a swivel angle based on a speed of the vehicle and a steering angle of the vehicle and then controls an actuator so that the actuator controls the direction of the light in accordance with the calculated swivel angle. For example, the direction of light turns right relative to the vehicle on a right-hand curved road and turns left relative to the vehicle on a left-hand curved road. Thus, the driver can clearly see a position in a heading direction of the vehicle in the night.
In particular, a front lighting system is described in US 2005/0047113A1 (JP 2005-96740A) which obtains the swivel angle for controlling the direction of the light by using multiple data maps which define a relation of the swivel angle to the speed and the steering angle.
Another front lighting system is proposed which calculates the swivel angle so that a ratio of the swivel angle to the steering angle gets larger as the speed of the vehicle gets higher. Such an operation of the conventional front lighting system is designed based on the fact that the driver of the vehicle looks at a position where the vehicle reaches after a particular period. The position where the vehicle reaches after the particular period gets more away from a current position of the vehicle as the speed of the vehicle gets higher. FIG. 10 is a data map defining a relation of the swivel angle to the steering angle for each of several values of the speed of the vehicle. For example, the swivel angle corresponding to 30° of the steering angle becomes 1.5° when the speed is 30 km/h and becomes 11° when the speed is 60 km/h.
However, when the vehicle turns right or left in an intersection shown in FIG. 11 with a low speed less than 30 km/h, the swivel angle becomes, as defined in the map in FIG. 10, too small to illuminate crosswalks 71 and 72 sufficiently in the intersection. For example, the maximum value of the swivel angle is 5° when the speed is 20 km/s. Therefore, the front lighting system has a difficulty in filling a need of drivers for better visibility around crosswalks in an intersection in the night.